Investigation of near-limit detonation propagation in a tube with helical spiral

The present study investigated the effect of wall roughness on the velocity, cellular structure, and limits of detonation propagation in tubes. Wall roughness was effected by placing a wire spring into the tube. Since the wire diameter is small compared to the tube diameter, the wire spiral is more representative of wall roughness than the repeated orifice plates used in the majority of previous studies. Detonation velocity was determined from the time-of-arrival of ionization probes spaced along the tube. Smoked foils were also inserted into the smooth section of the tube as well as immediately downstream of the rough section to record the cellular structure of the detonation wave. Premixed mixtures of C2H2 + 2.5O(2) + 70%Ar and C2H2 + 5N(2)O were used, which represent weakly unstable and unstable detonations, respectively. The initial pressure ranges of the experiments varied from 16 kPa (well within the detonation limits) to a few kPa at the limits. The present study indicates that wall roughness increases the velocity deficit, increases the cell size, as well as rendering the cellular structure more irregular. Wall roughness is also found to narrow the detonation limits in contrast to the conclusion of the previous studies.